I've known this guy for a while but not personally but almost Everytime I see him, if he interacts with me he does something physical letting me know i guess he's around. He'll stand directly behind me. He'll poke or pinch my lower back. He'll take his knuckles and rub my shoulder until I turn around or just put his hand on my shoulder/upper back sometimes talking if he does so low I can't hear him. It wasn't always like that. He used to talk to me as if he wasn't even talking to me by looking away and standing far apart then disappearing before I answer. he's stared at my butt a few times. he's friendly I presume, if he wanted more from me I think he's capable of being direct. I've seen him talk and touch other girls but why are our interactions more silent and physical.
I should also add due to the environment we're around each other I always think/know it's him so I don't really respond shocked. I usually try to wait for him to verbally say something and when he doesn't I just turn to face him he usually smiles then walks away.
And when I say lower back I mean before my actual butt starts but the side like the right side. And he's only done that once.